The CAM has been tested in six species of the Aeonium genus by studying the diurnal fluctuation of organic acids, pH and night fixation of CO2. The existence of a mesophyll structure able to support this metabolism has been shown as well as a congruent periodicity in the pool of cell starch.We have calculated the S, ES and Sm indices in the six species. A series of regression equations of different grades and types were calculated and shown to have correlation coefficients statistically significant. This allows us to confirm the suitability of the Sm index as a rapid test to establish the CAM as postulated by former authors.